There are several variables at play when it comes to pitching on a yeast cake. Like the first generation yeast health/viability, sanitation process/practices, fermentation health (originally), remaining viable cell count (pitching rate), % trub, etc...

That being said, I've had success pitching onto yeast cakes in the past, but I prefer to rinse the yeast prior to reuse if time permits.

I don't have a hemocytometer, so I can't count viable cells, but I try to make a best guess for pitching rates. If you start with healthy yeast initially, you'll be better off in the end.

The fermenter vessel could be the problem residually - if it is not perfectly sanitary and you leave the yeast cake in place and simply add wort to the vessel, over multiple reuses, there is a slightly greater likelihood of problems (all other things being equal) - that maybe wouldn't be exceeded by collecting the yeast and reusing a clean vessel for the re-pitch (with our without rinsing). No science there, just pragmatism, which I think the author was trying to get at (though a bit pompously, I admit). I routinely collect and repitch yeast at the rate of 1/3 cake for ales (in primary for up to a month) and 1/2 cake for lagers (in primary for a month, typically). I have reused a lager yeast (WLP800) up to 22 times adding yeast nutrient from Wyeast with each successive batch and not rinsing. So, maybe I'm lucky or maybe I'm careful, but that is what I have done. I believe I could reuse the unwashed primary and yeast cake without a problem, but I have decided not to risk it up til now - but I have been stepping up a Budejovice strain through successive pitches and a 3 gallon batch will be ready to move this weekend. Maybe I'll just bottle that and brew the next batch as a 5 gallon batch and pitch right on top of the cake...we'll see.

Hooey.If you have a sanitation problem it didn't come from reusing a yeast cake in this manner. Sounds like a confusion of correlation and cause.

Right.I pretty routinely repitch yeast through 8 or 9 brews with no issues whatsoever (and in the past, I've actually gone well beyond that, also with no problems. These days I play it safer).

Try pushing it experimentally. You'll know pretty quickly when you've reached your own brewery's limit. Only thing is, I wouldn't use the whole cake...1/3 to 1/2 is generally plenty, depending on the OG of the new beer.